crater

crater is an emulator for the Sega Game Gear, with an included Z80 assembler/disassembler, written in C.

Why?

While the internet is full of emulators for retro game systems, writing one is nevertheless a fun learning project.

crater is named after 31 Crateris, a star that was – for a short time in 1974 – misidentified as a moon of Mercury. Mercury was Sega’s codename for the Game Gear during development.

Installing

Only OS X and Linux are tested. You’ll need a modern compiler that supports C11 (clang preferred) and SDL 2. Using Homebrew, you can brew install sdl2; using apt, you can apt-get install libsdl2-dev.

Run make to create ./crater. To build the development version with debug symbols (they can exist simultaneously), run make DEBUG=1, which creates ./crater-dev. This also enables the printing of debugging info to stdout.

Usage

Running ./crater without arguments will display a list of ROM images located in the roms/ directory, and then ask the user to pick one, or enter their own ROM path. You can provide a path directly with ./crater path/to/rom.

Add or symlink ROMs to roms/ at your leisure. Note that they must end in .gg or .bin to be auto-detected.

Add --fullscreen (-f) to enable fullscreen mode, or --scale <n> (-s <n>) to scale the game screen by an integer factor.

Add --debug (-g) to display detailed information about emulation state while running, including register values and memory contents. You can also pause emulation to set breakpoints and change state.

./crater -h gives (fairly basic) command-line usage, and ./crater -v gives the current version.

Assembler/Disassembler

crater has built-in support for converting Z80 assembly into ROM images, as well as attempting the reverse process (i.e., disassembling).

--assemble <input> [<output>] (-a) converts source code into a .gg binary that can be run by crater. --disassemble <input> [<output>] (-d) executes the opposite operation. If no output file is given, crater will use the name of the input file, with the extension replaced with .gg for -a and .asm for -d. By default, this will never overwrite the original filename; pass --overwrite (-r) to let crater do so.